1. Field of the Invention
The present invention relates to antennas. More specifically, the present invention relates to millimeter wave reflect patch antennas and arrays thereof and components therefor.
2. Description of the Related Art
As noted by the Institute of Electrical and Electronic Engineers (IEEE): “The millimeter-wave region of the electromagnetic spectrum is usually considered to be the range of wavelengths from 10 millimeters (0.4 inches) to 1 millimeter (0.04 inches). This means they are larger than infrared waves or x-rays, for example, but smaller than radio waves or microwaves. The millimeter-wave region of the electromagnetic spectrum corresponds to radio band frequencies of 30 GHz to 300 GHz and is sometimes called the Extremely High Frequency (EHF) range. The high frequency of millimeters waves as well as their propagation characteristics (that is, the ways they change or interact with the atmosphere as they travel) make them useful for a variety of applications including transmitting large amounts of computer data, cellular communications, and radar.” See http://www.ieee-virtual-museum.org/collection/tech.php?id=2345917&lid=1.
For current more demanding applications, such as ‘active denial’, higher power millimeter waves, i.e. waves in the range of tens to thousands of watts, are required. Prior attempts to produce high power millimeter wave energy with solid-state devices have included waveguide and microstrip power combining. At millimeter wave frequencies, this method of combining typically produces unsatisfactory results due to heavy losses in the waveguide and/or microstrip medium.
Another approach is a spatial array technique. This technique has shown some promise. However, spatial arrays have not yet produced the power density levels that are required for the more demanding applications mentioned above.
One current approach involves the use of a reflect array amplifier. The reflect array has independent unit cells, each containing its own input antenna, power amplifier, and output antenna. These unit cells are then configured into an array of arbitrary size. Reflect arrays overcome feed losses by feeding each element via a nearly lossless free-space transmission path. As disclosed and claimed in U.S. patent application Ser. No. 10/734,445, entitled REFLECTIVE AND TRANSMISSIVE MODE MONOLITHIC MILLIMETER WAVE ARRAY SYSTEM AND IN-LINE AMPLIFIER USING SAME, filed Dec. 12, 2003 by K. Brown et al. (Atty. Docket No. PD 01W176A), the teachings of which are hereby incorporated herein by reference, reflect arrays differ from conventional arrays in that the input signal is delivered to the face of the array via free space, generally from a small horn antenna.
An active reflect array consists of a large number of unit cells arranged in a periodic pattern. Each reflect array element is equipped with two orthogonally-polarized antennas, one for reception and one for transmission. That is, reflect arrays typically receive one linear polarization and radiate the orthogonal polarization, e.g., the receive antenna receives only vertically-polarized radiation and the transmit antenna transmits only horizontally-polarized radiation.
When integrated with the power-generating electronics on a thin semiconductor substrate, such antennas tend to have narrow bandwidths and high losses due to large surface currents. The size of each unit cell is constrained by the need to avoid grating lobes; for a fixed array whose main beam is in the broadside direction, each unit cell may be no more than approximately 0.8 wavelengths on a side.
Higher power levels are attained by combining the outputs of multiple transistors. The drawback of this approach is that the power combiners themselves take up valuable area on the semiconductor wafer that could otherwise be occupied by power-generating circuitry.
Hence, a need remains in the art for improved systems and methods for generating high power millimeter wave beams. Specifically, a need remains in the art for a reflect array antenna capable of generating high power millimeter wave energy without significant loss.